Allocating resources for shared and non-shared downlink wireless resources

ABSTRACT

A wireless network dynamically allocating a timeslot to a downlink dedicated channel to a user equipment (UE) in a cell is disclosed. A call may be reallocated a different timeslot midcall where the different timeslot has a highest quality rank in the cell. The timeslot may then be allocated to a downlink shared channel in the cell. The allocation of the timeslot to the downlink dedicated channel may be prioritized over the allocation of the timeslot to the downlink shared channel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national phase application of InternationalApplication No. PCT/EP2005/051549, filed Apr. 7, 2005, which claimspriority to United Kingdom Application No. 0408202.0, filed Apr. 13,2004, the contents of which are hereby incorporated by reference intothe present disclosure in their entirety.

FIELD OF THE INVENTION

This invention relates to communication systems and particularly (thoughnot exclusively) to dynamic channel assignment in cellular communicationsystems such as 3GPP (3^(rd) Generation Partnership Project) radiocommunication systems.

BACKGROUND OF THE INVENTION

In UTRA (Universal Mobile Telecommunication System Terrestrial RadioAccess) TDD mode within 3GPP, both dedicated and shared channels aresupported. Dedicated channels give a reserved resource to a user, incontrast to shared channels in which a pooled resource is dynamicallyshared amongst users. Dedicated channels are best suited to nearconstant bandwidth traffic, typically speech or streamed audio/video.Shared channels are more suited to bursty traffic, typically packet dataservices such as internet traffic.

In UTRA TDD mode, when a dedicated channel (DCH) is admitted, physicalresources (channelisation codes and timeslots) are reserved for itsexclusive use. This reservation is often called channel allocation. Twoforms of channel allocation are employed:

-   -   fixed channel allocation (FCA)    -   dynamic channel allocation (DCA).

In FCA, the codes and timeslots for the DCH are selected at random fromthose available in the cell.

In DCA, the code and timeslot assignment is intelligent. The followingclassification of DCA schemes is known, for example from the publicationby H. Haas and S. McLaughlin “A dynamic channel assignment algorithm fora Hybrid TDMA/CDMA-TDD interface using a novel TS-opposing technique” inIEEE J. Sel. Areas Comms. 19(10) 2001:

-   -   Traffic-adaptive channel allocation: based upon the traffic        loading on neighbouring cells, a common pool of channels (codes        and timeslots) is shared such that heavily loaded cells receive        more channels. Adjusting the downlink-uplink timeslot division        in a cell(s) may also be considered here. (note that if the        division is not equal in every cell then UE-UE (remote        station-remote station) and Node B-Node B (base station-base        station) interference sources arise).    -   Re-use partitioning: this may be employed when an operator has a        number of carriers which may be deployed in a re-use pattern.    -   Interference-based DCA: channels are assigned based upon        interference power measurements at the Node B or the UE. These        schemes match well to TD-CDMA which is typically interference        limited, and they may be deployed in a decentralised        architecture giving low algorithmic complexity.

DCA schemes may be either centralised or decentralised. A centralisedalgorithm would be located at the RNC (Radio Network Controller) andwould exploit measurements made at a number of Node B's and UEs in itsdecision making. The impact of an admission in one cell on theperformance of admitted connections in the same and other cells may bedetermined. Resources from a number of cells may be considered on acollective or pooled basis. Such an algorithm requires significantsignalling, may be computationally complex, and may not scale as thenumber of cells under the RNC is increased.

A decentralised algorithm manages DCH admissions for a single cell(typically). It is located at the RNC, where admission is performed, andwhere measurements are available. The complexity is considerablyreduced, and scaling considerations are easy to estimate (the totalcomplexity for the RNC is proportional to the number of cells under theRNC).

DCA may also be used to reassign the resources of calls in progress topermit the admission of new calls, or to improve their QoS. For example,a voice user may be experiencing high interference in one timeslot, andthe DCA algorithm may reassign the user to another timeslot which haslower interference levels.

Call Admission Control

DCA works very closely with Call Admission Control (CAC). Execution of aCAC algorithm is required when UEs are supported with some guarantees ofquality of service. Users of 3GPP traffic class=“Interactive” onlyexpect to receive better service than other interactive users withlesser traffic handling priority, whilst users of 3GPP trafficclass=“background” have no expectations (this is truly best effort).However, users of 3GPP traffic class=“conversational” or “streaming”have delay and bandwidth requirements. The CAC needs to balance theconflicting requirements of low blocking probability and low droppingprobability. Dropping occurs when an ongoing call is prematurelyterminated and is perceived by users as more objectionable than blocking(when the system does not allow a call to be initiated in the firstplace): the blocking probability is thus set higher than the droppingprobability. The CAC maintains the loading on the network below athreshold level such that the dropping probability is acceptable.

Network loading may be measured in terms of:

-   -   number of UEs admitted (of each traffic class/quality of service        parameters)    -   Node B interference (uplink)    -   Node B transmit power (downlink)

Interference is composed of two parts, intracell interference arisingfrom transmissions to/from UEs attached to the same cell, and intercellinterference arising from transmissions to/from UEs attached to othercells.

CAC is needed:

-   -   on new call attempts    -   on handovers    -   on channel reallocation initiated by DCA.

In the publication “D06: Conceptual studies on Radio Resource and QosManagement Algorithms” (available at web addresshttp://www.arrows-ist.upc.es/publications/deliverables/Summary_Arrows-D06.pdf),a distinction is drawn between DCA and CAC. A first DCA algorithmdescribed in this application maintains an ordered list of timeslotswhich should be considered when an admission is to be made (this couldbe a new call, a handover, or a reallocation). The CAC takes a timeslotfrom the top of this list and evaluates whether the addition of the UEinto this timeslot would generate acceptable interference to existingcalls. Additionally, a second DCA algorithm can identify calls forreallocation from one timeslot to another—for example, to improve speechquality. However, this publication does not enable dedicated and sharedchannels to coexist.

Coexistence of Dedicated and Shared Channels

Although the coexistence of dedicated channels (managed by DCA) andshared channels (managed by a radio scheduler) has not been addressedfor 3GPP TDD, in the past, to the knowledge of the inventors hereof,clearly there are two possible methods of assigning the codes andtimeslots to dedicated and shared channels:

-   -   segregation: slots are used exclusively by either dedicated or        shared channels    -   mixing: slots support both dedicated and shared channels at the        same time.

A discussion of a possible interference based DCA technique is includedin 3GPP specification TR 25.922 (available from the websitewww.3gpp.org). The method is based upon interference measurements madeby the UE and the Node B (timeslot Interference Signal Code Power orISCP, i.e., intercell interference). The algorithm is decentralised andlocated at the RNC. The algorithm covers both slow DCA and fast DCA.Slow DCA involves adjustments to the DL/UL (downlink/uplink) splitacross cells. The DL/UL split is adjusted for each cell independently ofother cells. Fast DCA allocates resources more rapidly. Code pooling andtimeslot pooling are discussed (in code pooling a DCH is allocated anumber of codes in the same timeslot, whilst in timeslot pooling asingle code and multiple timeslots are used). Channel reallocation(intra-cell handover) can be triggered to cope with varying interferenceconditions, or to reduce fragmentation of codes and timeslots that a DCHuses. UE measurements to support DCA include ISCP, path lossmeasurements, link quality measurement and UE transmit power values.

In the publication “D06: Conceptual studies on Radio Resource and QosManagement Algorithms” referred to above and in the publication by M.Haardt et al., “The TD-CDMA based UTRA TDD Mode”, IEEE J Sel Areas Comms18(18), August 2000, the DCA algorithm generates a priority list oftimeslots according to long and short term recording and statisticalevaluation of interference, at the UE and the Node B. This is used bythe CAC. The DCA algorithm described reallocates resources to minimisethe number of timeslots used. However, these publications do not enablededicated and shared channels to coexist.

In the publications by Berg, “Maintaining high capacity for centralisedDCA with limited measurements and signalling”, PIMRC 1999, and “Radioresource management in bunched personal communication systems”, PhDThesis, March 2002, Royal Institute of Technology, Stockholm, acentralised DCA algorithm has been evaluated that exploits knowledge ofthe gain matrix (the matrix of path gains between UEs and Node B's) andthe transmit power of each UE. The method ensures that all SIR targetsare met, or the new call is not admitted. The first of thesepublications suggests ways to compensate for gaps in the gain matrix—byusing values taken by other UEs in the same cell, or by setting a higherSIR target for the new admission than necessary and allowing the powercontrol to adjust this during the call. A third method discards the gainmatrix approach and instead admits the UE to the timeslot in which itmeasures the minimum interference. However, such gain matrixcalculations are complex.

In the publication by I. Forkel et al., “Dynamic channel allocation inUMTS Terrestial Radio Access TDD systems”, VTC 2001, the admissionattempt is made into the DL and UL timeslots with the minimuminterference. The admission is allowed if the interference levels in thetwo directions are below their respective threshold values (these can beservice type dependent). A more advanced scheme allows the allocationfor a voice call to be changed if the bit error rate (BER) exceeds athreshold for a given duration. The DCA scheme gives C/I gains over FCAbut little voice capacity improvement. Furthermore, this publicationdoes not enable dedicated and shared channels to coexist, and the DCAand CAC metrics are crude.

In the publication by I. Forkel & T. Kriengchaiyapruk, “Management ofcircuit and packet switched data in UMTS terrestrial radio accessnetworks”, 3G Wireless 2001, a ‘timeslot scoring method’ is appliedwhere a timeslot is chosen at random from the set of timeslots whoseinterference falls below a threshold, and have sufficient capacity. Inthis technique, code pooling is used, otherwise the DCA and the CACwould be more complex and less reliable. However, this publication doesnot enable dedicated and shared channels to coexist.

From patent publication EP0817521, “Interference based dynamic channelassignment”, it is known to use long and short term interferencemeasurement lists on DL and UL. The algorithms are decentralised, on aper cell or per sector basis.

From patent publication EP0986928, “DCA method in a cellular radiocommunication network”, it is known to maintain priority indices basedupon periodic measurements of radio parameters. This publication isorientated to a frequency channel assignment. However, this publicationdoes not enable dedicated and shared channels to coexist and itsapplication to timeslot assignment is not clear.

In patent publication EP1063791, “CDMA communication method using adynamic channel code assignment, and a base station performing themethod”, a channelisation code used by a UE is changed in response tointerference measurements. However, this publication is restricted to alimited algorithm for an FDD (Frequency Division Duplex) system.

There are known a number of publications involving Call AdmissionControl for WCDMA, but these are generally oriented towards 3GPP FDD(Frequency Division Duplex) mode. In the publication by H. Holma & A.Toskala (editors), “W-CDMA for UMTS”, John Wiley, 2000, an interferencebased algorithm is described for the FDD mode. On the uplink, theexpected interference at the Node B after admission is compared to athreshold. The difficulty is in estimating how much additionalinterference is generated by the new admission. Two solutions aredescribed, the derivative and integral methods which both exploitknowledge of the shape of the interference versus load curve I=1/(1−η)where η is the load). On the downlink the expected transmit powerfollowing admission is compared to a threshold. The increment in poweris estimated by an open loop calculation. The downlink algorithm isapplicable to the TDD mode. The uplink algorithm is not applicable toTDD mode since in TDD mode, the Node B detector eliminates most of theintracell interference (thus adding another user to a TDD cell will notincrease the detected Node B interference in that cell).

In the publication by J. Lee & Y. Han, “Downlink admission control formultimedia services in WCDMA”, IEEE International Symposium on Personal,Indoor and Mobile Radio Communications (PIMRC) 2002, a simple downlinkmethod is described that uses a transmit power threshold value.

There are a number of papers where uplink CAC is based on Node Binterference estimation. They differ in the method in which theinterference increment is calculated, and also in whether the impact onthe serving cell or on neighbouring cells is included too. Thepublication by Kim et al., “SIR-based call admission control byintercell interference prediction for DS-CDMA systems”, IEEE Comms.Letters, 4(1), 2000, extends the work of Z. Liu and M. E. Zarki in thepublication “SIR-based call admission control for DS-CDMA systems”, IEEEJ. Sel. Areas Comms., 12, 1994 to base an algorithm on ‘ResidualCapacity’, which expresses the number of calls which can be accepted ineach cell following the admission of the user in question. The residualcapacity is calculated for the intended serving cell and all theneighbours for which the UE is able to make pilot/beacon measurementsof. If the residual capacity is greater than or equal to 1 for allcells, then the call is admitted. This method may be useful if the SIRneeds of the UEs are the same and sufficient measurements are availableto the algorithm. The complexity is moderate. However, this method islimited by the restriction of equal SIR needs and inappropriatelyincludes intracell interference in its workings.

In the publication by N. Dimitrou & R. Tafazolli, “Quality of servicefor multimedia CDMA”, IEEE Comms. Mag. July 2000, there is presented asimple uplink CAC algorithm based on an interference threshold, whichcan consider the impact on the local cell or on multiple cells. However,this algorithm is relatively inaccurate and unsophisticated.

In the publication by F. Gunnarsson et al., “Uplink admission control inWCDMA based on relative load estimates”, International conference oncomms. 2002, a formula is derived for the relative (uplink) load on acell as a function of the SIR target of the service, the path gainbetween each UE and its serving site, and the path gain between the UEand the cell in question. The CAC algorithm calculates the new relativeload in each cell which would follow an admission, and compares thesevalues against a threshold. The relative load in cell j is:

${\hat{L}}_{j} = {\sum\limits_{i = 1}^{M}\;\frac{{CTIR}_{i}g_{ij}}{g_{ik}}}$

-   -   where    -   i is the mobile number, ranging from 1 to M, in the system,    -   CTIR_(i) is the target value of the carrier to total        interference ratio for mobile i at its serving site, k,    -   g_(ij) is the path gain from mobile i to cell j,    -   g_(ik) is the path gain from mobile i to its serving site, cell        k.

A call is admitted provided the relative load is less than the thresholdfor each cell considered. The authors claim that measurements of pathgain are more accurate than those of noise or interference at the Node B(as used in the publication by Kim et al., “SIR-based call admissioncontrol by intercell interference prediction for DS-CDMA systems”,referred to above). If a mobile is too distant to be able to measure thebeacon of a cell it is not included in the relative load calculation forthat cell. Measurement load is minimised by relying upon initialmeasurements and thereafter those available at handover. Cell centre UEsoffer few measurements (no handovers) but their interferencecontribution is less than those of cell edge UEs. The approach may beused for multiple services (the CTIR value is changed appropriately).This paper considers FDD where intracell interference cannot becancelled and is not directly applicable to TDD for the serving cell.

Thus, although many different algorithms are known for channelallocation, these are not optimal for all conditions and systems. Inparticular, known channel allocation schemes are not ideally suited forcommunication systems comprising both shared and dedicated communicationchannels.

Hence, an improved system would be advantageous and in particular asystem allowing increased flexibility, improved performance, improvedutilisation of shared and dedicated channels and/or improved suitabilityof a range of communication systems including TDD communication systemswould be advantageous.

STATEMENT OF INVENTION

Accordingly, the Invention seeks to preferably mitigate, alleviate oreliminate one or more of the above mentioned disadvantages singly or inany combination.

In accordance with a first aspect of the present invention there isprovided a method of allocating a dedicated communication channel in acellular communication system.

In accordance with a second aspect of the present invention there isprovided an apparatus of allocating a dedicated communication channel ina cellular communication system.

In accordance with a third aspect of the present invention there isprovided a method for dynamic channel assignment in a TDD radiocommunication system.

In accordance with a fourth aspect of the present invention there isprovided an arrangement for dynamic channel assignment in a TDD radiocommunication system.

The invention may allow an improved channel allocation in cellularcommunication systems and may in particular provide for an improvedallocation of shared and dedicated communication channels. The inventionmay additionally or alternatively allow an efficient and low complexityimplementation.

By one approach the disclosed concepts will include the step ofallocating a channel timeslot for use as a dedicated channel by:

testing each of a plurality of selected shared channel timeslots forcode resource acceptability, transmit power acceptability and intercellinterference acceptability; and

if the testing fails selecting a shared channel timeslot with lowesttimeslot number and testing the selected shared channel timeslot fortransmit power acceptability and intercell interference acceptability.

It will be appreciated that in some embodiments the present invention isbased on interference based DCA, concerns a DCA method that isdecentralised for the downlink but centralised in the uplink, includesCAC algorithms, and employs a segregation of dedicated and sharedchannels.

BRIEF DESCRIPTION OF THE DRAWING(S)

One dynamic channel assignment scheme for TDD radio communicationnetworks with coexisting dedicated and shared channels incorporating thepresent invention will now be described, by way of example only, withreference to the accompanying drawing(s), in which:

FIG. 1 shows a block schematic diagram illustrating a 3GPP radiocommunication system in which the present invention may be used;

FIG. 2 shows a block schematic diagram illustrating timeslot allocationof the TDD frame in the system of FIG. 1, incorporating the presentinvention;

FIG. 3 shows a block schematic diagram illustrating uplink CAC flow inthe system of FIG. 1, incorporating the present invention;

FIG. 4 shows a block schematic diagram illustrating downlink CAC flow inthe system of FIG. 1, incorporating the present invention; and

FIG. 5 shows a block schematic diagram illustrating slot allocation toDCH and DSCH in the system of FIG. 1, incorporating the presentinvention.

DESCRIPTION OF PREFERRED EMBODIMENT(S)

The following preferred embodiment of the present invention will bedescribed in the context of a UMTS Radio Access Network (UTRAN) systemoperating in TDD mode. However, it will be appreciated that theinvention is applicable to many other communication systems.

Referring firstly to FIG. 1, a typical, standard UMTS Radio AccessNetwork (UTRAN) system 100 is conveniently considered as comprising: aterminal/user equipment domain 110; a UMTS Terrestrial Radio AccessNetwork domain 120; and a Core Network domain 130.

In the terminal/user equipment domain 110, terminal equipment (TE) 112is connected to mobile equipment (ME) 114 via the wired or wireless Rinterface. The ME 114 is also connected to a user service identitymodule (USIM) 116; the ME 114 and the USIM 116 together are consideredas a user equipment (UE) 118. The UE 118 communicates data with a Node B(base station) 122 in the radio access network domain 120 via thewireless Uu interface. Within the radio access network domain 120, theNode B 122 communicates with an radio network controller (RNC) 124 viathe Iub interface. The RNC 124 communicates with other RNC's (not shown)via the Iur interface. The Node B 122 and the RNC 124 together form theUTRAN 126. The RNC 124 communicates with a serving GPRS service node(SGSN) 132 in the core network domain 130 via the Iu interface. Withinthe core network domain 130, the SGSN 132 communicates with a gatewayGPRS support node (GGSN) 134 via the Gn interface; the SGSN 132 and theGGSN 134 communicate with a home location register (HLR) server 136 viathe Gr interface and the Gc interface respectively. The GGSN 134communicates with public data network 138 via the Gi interface.

Thus, the elements RNC 124, SGSN 132 and GGSN 134 are conventionallyprovided as discrete and separate units (on their own respectivesoftware/hardware platforms) divided across the radio access networkdomain 120 and the core network domain 130, as shown in FIG. 1.

The RNC 124 is the UTRAN element responsible for the control andallocation of resources for numerous Node B's 122; typically 50 to 100Node B's may be controlled by one RNC. The RNC also provides reliabledelivery of user traffic over the air interfaces. RNC's communicate witheach other (via the Iur interface) to support handover andmacrodiversity.

The SGSN 132 is the UMTS Core Network element responsible for SessionControl and interface to the HLR. The SGSN keeps track of the locationof an individual UE and performs security functions and access control.The SGSN is a large centralised controller for many RNCs.

The GGSN 134 is the UMTS Core Network element responsible forconcentrating and tunnelling user data within the core packet network tothe ultimate destination (e.g., internet service provider—ISP).

Such a UTRAN system and its operation are described more fully in the3GPP technical specification documents 3GPP TS 25.401, 3GPP TS 23.060,and related documents, available from the 3GPP website at www.3gpp.org,and need not be described in more detail herein.

In some embodiments, as described in greater detail below, the presentinvention is based on realisations of different co-operating DCA and CACalgorithms for a TDD system in which the timeslots are individually usedby dedicated or shared channels only (timeslot segregation is applied).In other words there are no timeslots in which dedicated and sharedchannels exist together. For convenience, the algorithms will bereferred to as DCA1, DCA2 and CAC. Besides the algorithms themselves,the described embodiments also include the dynamic management of thetimeslot allocation to dedicated and shared channel use, in response totraffic needs. Thus, the described embodiments may allow an improvedutilisation of shared and dedicated communication channels therebyproviding a more efficient resource utilisation and thus increasedcapacity of the cellular communication system as a whole.

The timeslot allocation of the TDD frame 200 is shown in FIG. 2. In thisfigure, uplink timeslots 210 that are used for shared channels arelabelled “USCH”, downlink timeslots 220 that are used for sharedchannels are labelled “DSCH”, uplink timeslots 230 that are used fordedicated channels are labelled “UL_DCH”, downlink timeslots 240 thatare used for dedicated channels are labelled “DL_DCH”. The figure alsoshows 3 types of timeslot that are required to support TDD operation: a“BCH” timeslot 250 is used for broadcast information, a “S-CCPCH”timeslot 260 is used for forward access information and the “RACH”timeslot 270 is used for random access by the UE.

It should be noted that the DL DCH slots 240 need not be continuous, asdrawn in the figure, but may be interspersed with DSCH slots 220(similarly for the uplink).

It should be noted that the division between DL and UL is assumed to befixed and equal in all cells in the following description, but it willbe understood that many aspects of the invention are applicable to adynamic division between the two directions.

It will further be noted that the particular timeslot usage shown in thefigure is exemplary, and that a different arrangement of slots(including the use of multiple divisions between downlink and uplink)are also possible.

The minimum number of DCH slots for each direction is zero, and themaximum number (n_(DL) _(—) _(DCH) _(—) _(MAX)/n_(UL) _(—) _(DCH) _(—)_(MAX)) is a function of the number of DL/UL slots (n_(DL)/n_(UL)) (setby an Operations and Maintenance (OAM) function, the OAM function beinga device—typically a computer—that allows an operator to set parametersfor network operation) and the admittance of traffic on shared channelswith delay guarantees. This can be explained as follows. The sharedchannels may carry traffic of conversational or streaming traffic classwhich possess delay guarantees. In order to ensure the meeting of theseguarantees, one or more slots should be secured for the shared channels.Of course, this number (n_(DSCH) _(—) _(RESERVED)/n_(USCH) _(—)_(RESERVED)) will fluctuate according to the admitted traffic on sharedchannels of this nature, it may be zero. Thus:n _(DL) _(—) _(DCH) _(—) _(MAX) =n _(DL) −n _(DSCH) _(—) _(RESERVED)n _(UL) _(—) _(DCH) _(—) _(MAX) =n _(UL) −n _(USCH) _(—) _(RESERVED)

Furthermore, in the described embodiments, the number of DCH timeslotsat any one time, and in a given cell, is controlled by the DCA and CACalgorithms, as described below. Essentially, the algorithm adjusts thenumber to accommodate the traffic loading on the dedicated channels, butsubject to the maximum number (n_(DL) _(—) _(DCH) _(—) _(MAX)/n_(UL)_(—) _(DCH) _(—) _(MAX)). The initial number of DL and UL DCH slotsshould be zero. Thus, the algorithms ensure that, if possible, thenumber of DCH channels is automatically adjusted in response to thetraffic requirement for dedicated channels.

It will appreciated that the embodiments exploit the fact that themultiuser detector-based TDD receiver eliminates intracell interferenceand that intercell interference is dominant.

The algorithms DCA1, DCA2 and CAC on which the described embodiment ofthe present invention is based, will now be described in more detail.

DCA1

This algorithm identifies the best candidate timeslot(s) for newadmissions (this may be a new call attempt, a handover or a midcallreallocation). The candidate timeslots are held in an ordered list—theCAC algorithm then takes timeslot(s) from the head of this list when anew admission attempt is to be processed. Thus, DCA1 determines aranking for a plurality of communication channels designated as DCHchannels. To maintain the ordered list (in many embodiments a separatelist is maintained for the uplink and downlink), measurements areperformed by the UE and the Node B, and passed to the algorithm (at theRNC). The measurements may be used to determine interference levels andthe ranking may be in response to the interference levels.

DCA1 Downlink

When an admission attempt is to be processed, the UE concerned isinstructed to perform ISCP (Interference Signal Code Power, a measure ofintercell interference) measurements for the existing (in use) DL DCHtimeslots in the prospective serving cell of the UE (there are n_(DL)_(—) _(DCH) timeslots).

The UE also measures and reports the P-CCPCH (Primary Common ControlPhysical Channel) RSCP (Received Signal Code Power) for the prospectiveserving cell (the P-CCPCH RSCP is the received code power for a beaconchannel that can be received throughout the cell). The UE sends thesemeasurements to the RNC and the RNC orders the timeslots in terms ofincreasing ISCP.

DCA1 Uplink

All the Node B's under the RNC are instructed to measure ISCP for allpossible uplink DCH timeslots (i.e., over n_(UL) _(—) _(DCH) _(—) _(MAX)slots). In the uplink, the ISCP is the uplink intercell interferencemeasured at the Node B.

In one aspect of the described embodiment of the present invention, themetric for uplink DCA1 accounts for the dominance of intercellinterference in TDD. This is based on two metrics (“metricA” and“metricB”), which are described below.

The algorithm maintains an ordered list of timeslots in increasing orderof the metric, metricA (below), for each cell under the RNC. It will beunderstood that a subset of these cells could be used if required toease computational complexity. The list is restricted to the timeslotscurrently in use by the UL DCHs in that cell, and updated following newmeasurement reports.

${metricA}_{j,t} = {\sum\limits_{{n = 1},{n \neq j}}^{N}\;{ISCP}_{n,t}}$where

-   -   t is the timeslot,    -   n is the cell number,    -   j is the prospective serving cell,    -   N is the number of cells under the RNC, and    -   ISCP_(n,t) is the intercell interference at cell n in timeslot t

An alternative metric, metricB, is presented below. This metricestimates the maximum value of the ISCP across the set of cells underthe RNC for each cell following the admission of UE i.

The expected interference at cell n≠j in timeslot t following theadmission of the UE i in cell j is:I _(n,t) =ISCP _(n,t)(1+SIR _(tgt) g _(in) /g _(ij))where

-   -   SIR_(tgt) is the SIR (Signal to Interference Ratio) target for        UE i,    -   g_(in) is the path gain from UE i to cell n≠j, and    -   g_(ij) is the path gain from UE i to cell j

The metricB determines the maximum value of the expected interferenceacross the cells:metricB _(j,t)=max_(n≠j)(I _(n,t))

Timeslots are ordered in increasing order of metricB.

DCA2

DCA2 manages DCH resources midcall. It may be used to identify DCHs thatshould be reallocated from one timeslot to another, for example, toimprove the quality of service (QoS) of the radio bearer, or to groomthe interference across the slots to improve the likelihood ofsuccessful future admissions (and thus maximising the system capacity).DCA2 uses the list of timeslots maintained by DCA1 as candidates for newslot(s) to be used. It then calls CAC to check that this timeslot(s) maybe used.

Thus, the DCA2 algorithm may monitor ongoing calls and may determinethat it is desirable to switch a call to another communication channelin the form of a different time slot. The highest ranked time slot maythen be used and the feasibility of using this time slot is evaluated bythe CAC algorithm as described later.

Specific uses of DCA2 are given below:

Midcall Reallocation to Alleviate Outage of a UE

The RNC is able to identify when a UE is about to move into “outage”when its quality of service needs are not met, by the following means:

-   -   a) it has hit its maximum (uplink) transmit power. The RNC is        able to identify when this occurs by a measurement report that        is sent from the UE to the RNC,    -   b) the block error rate is significantly above the target (this        is called a radio link failure in 3GPP).

If this occurs, in the prior art, the RNC moves the UE to a differenttimeslot(s) (the RNC would move the UE to a timeslot where there is lessinterference, such that the UE may transmit at a lower power to achievean identical signal to interference ratio). However, in the preferredembodiment of the present invention, when the RNC identifies that the UEis about to move into outage, it spreads the UE transmissions over moretimeslots such that the transmit power needed in any individual slot isreduced.

As an example of this aspect, if a speech UE (using a dedicated channel)was admitted when it did not lie at the cell edge, and was granted twounits of physical resource in one timeslot on the uplink (as an examplein 3GPP TDD, the UE could be granted a single SF8 code and onetimeslot), moves to the cell edge it is given an additional timeslotwith a single unit of physical resource (as an example, a single SF16code in the case of 3GPP TDD), and the amount of physical resource inthe original timeslot is reduced to a single unit (for example, in thecase of 3GPP TDD, the original code is reallocated to SF16). Thereby, bymoving the transmission from one to two timeslots the transmit power ofthe UE in a timeslot is halved, but the data link to the UE ismaintained at the original data rate.

End of a Call

In the described embodiment, at the end of a call, if the freeing of thededicated channels used by that speech call results in a new unusedtimeslot, that timeslot is released for use by shared channels. Thus, ona determination of a cease of the demand for the DCH, the communicationchannel, in the form of the time slot, is re-allocated as a shared timeslot. This will ensure a dynamic distribution between shared anddedicated channels that will match the current traffic requirements. Thedescribed embodiment may further allow a higher prioritisation ofdedicated channels than shared channels until the maximum number ofdedicated channels is allocated.

CAC

CAC is called when there is a new admission attempt (new call, handover,midcall reallocation). It takes timeslot(s) suggested by DCA1 and teststo see if the new admission in the suggested timeslot would lead to anoutage or not. Thus, the CAC algorithm performs a feasibility test for atest time slot to determine if this time slot is suitable for allocationas the required DCH. The test time slot is sequentially selected as thenext time slot in the ranked list.

In the specific example, every Node B sends measurement reports to theRNC of the carrier power, P_(carrier), for all possible DL DCH timeslots(there will be n_(DL) _(—) _(DCH) _(—) _(MAX) such measurement reports).

On an admission attempt, the uplink and/or downlink admission stepsbelow are taken.

Uplink CAC

In the preferred embodiment of the invention, the flow chart 300 in FIG.3 shows the sequence of steps for uplink CAC. The flow chart isdescribed in terms of 3GPP terminology where a DCH is a dedicatedchannel and an USCH is an uplink shared channel.

After start, each timeslot is taken (steps 310 and 350) in turn from theDCA1 list and tests (1) to (3)—steps 320 to 340—(described below) areapplied to the timeslots until a timeslot is found for which all testsare passed. Thus, the ranked time slots are sequentially selected astest time slots in the order in which they are ranked. The sequentialselection continues until a time slot is found which passes thefeasibility test. If no time slots are found that meets the feasibilityrequirements, a time slot designated as a USCH is re-designated as aDCH. This time slot is then tested and if it meets the feasibilityrequirement, it is allocated as the required DCH.

Thus, if all timeslots fail, a new timeslot is provisionally acquiredfor UL DCH if the maximum number of UL DCH slots (n_(UL) _(—) _(DCH)_(—) _(MAX)) has not been reached (step 360). In an aspect of thepreferred embodiment of the invention, in such circumstances, the USCHslot with the smallest available timeslot number is sacrificed(provisionally) for DCH (step 370). Selecting the smallest availabletime slot number in a system where DCH channels are allocated first inthe frame (lower time slot numbers) and USCH channels are allocated lastin the frame (higher time slot numbers) will allow the DCH channels tobe grouped together. It will be appreciated that in systems havingdifferent configurations, other grouping criteria may be used.

This policy of grouping DCH time slots, when applied across the one ormany RNCs, aims to place the DCH slots before the USCH slots in allcells as far as possible. This makes interference measurements used byDCA1 more reliable since DCH slots with approximately constant bandwidthare aligned across cells. Tests (2) and (3) (steps 380 and 390) are thenperformed with this newly released slot (test (1) is not required sincethere is no DCH resource in the new slot). If either test fails the CACis deemed to have failed and the provisionally acquired timeslot isreturned to USCH usage.

Although the tests (1) to (3) in the flow chart of FIG. 3 are describedbelow in terms of 3GPP TDD, it will be understood that these tests aregenerally applicable to other TDD systems. The tests are as follows:

Test (1) Availability of Code Division Multiple Access code: Checkuplink code resource in the timeslot (the RNC must ensure that there isa spare CDMA code(s) for use by the UE in the uplink). Typically up to100% of the code space can be used, for example, 8 codes at SF8, butthis ceiling may be reduced by the OAM.

Test (2) Availability of user equipment transmit power: Calculate theexpected transmit power of the UE i to the prospective serving cell j inaccordance with the following formula:

$p_{ij} = \frac{{SIR}_{{tgt},i}\left( {{ISCP}_{{j,t}\;} + N_{{th},j}} \right)}{g_{ij}}$where

-   -   SIR_(tgt,i) is the SIR target for the service of UE i,    -   ISCP_(j,t) is the ISCP measured by the Node B j in timeslot t,    -   g_(ij) is the pathgain from UE i to cell i, and    -   N_(th,j) is the thermal noise power at Node B j.

This is an approximation: it is assumed that the intracell interferenceis zero, that the SIR will match the target, and that the intercellinterference will not increase following the admission. Note, thethermal noise power may be measured at the Node B (and passed to the RNCvia OAM), or the worst case value within the specification may beassumed.

p_(ij) is compared with the maximum transmit power of the UE.

Test (3) Acceptability of resulting interference level: Check on whetherthe intercell interference levels at the cell sites will be acceptableafter the admission: relative load calculation. In the publication“Uplink admission control in WCDMA based on relative load estimates”referred to above, the relative load calculation includes intracell andintercell interference. In this aspect of the preferred embodiment ofthe present invention, the relative load calculation accounts for thefact that there is no intracell interference at the Node B after theNode B has detected the TDD signal (see equation below). The differenceis incorporated by restricting the set of terms included in thesummation.

Inputs to the test are:

-   -   path gain measurements from each admitted mobile transmitting in        timeslot t to all neighbour cells (the UE will only take        measurements on the strongest neighbours, path gains to other        cells will be assumed to be zero)    -   path gain measurements from candidate mobile i to all neighbour        cells (the UE will only take measurements on the strongest        neighbours, this is set N_(i))    -   calculation of the existing relative load on each cell n, in        timeslot t, {circumflex over (L)}_(n,t) as

${\hat{L}}_{n,t} = {\sum\limits_{{m = 1},{m \notin S_{n}}}^{M_{t}}\frac{{SIR}_{{tgt},m}g_{mn}}{g_{mk}}}$

-   -   where    -   m is the mobile number, ranging from 1 to Mt, in the system        transmitting in timeslot t,    -   S_(n) is the subset of the Mt mobiles that are served by cell n,    -   SIR_(tgt,m) is the signal to interference ratio target for        mobile m,    -   g_(mn) is the path gain from mobile m to cell n, and    -   g_(mk) is the path gain from mobile m to its serving site, cell        k.

The algorithm used is as follows:

-   -   Calculate the new relative load for all cells for which path        gain measurements are available from UE i (but excluding cell j,        the prospective serving cell for UE i), ∀nεN_(i), in accordance        with the following formula

${\hat{L}}_{n,{t\mspace{11mu}{NEW}}} = {{\hat{L}}_{n,{t\mspace{11mu}{OLD}}} + {\frac{{SIR}_{{tgt},i}g_{i\; n}}{g_{ij}}.}}$

-   -   Admit the user if {circumflex over (L)}_(n,t,NEW)≦L_(max),        ∀nεN_(i). L_(max) is typically a parameter that may be set at        the OAM. The typical range of values for L_(max) is 0≦L_(max)≦1.        Downlink CAC

The flow chart 400 in FIG. 4 shows the sequence of steps of downlink CACin accordance with the preferred embodiment of the present invention. Itmay be noted that this flow chart 400 shown in FIG. 4 for downlink CACflow is similar to the flow chart 300 for uplink flow shown in FIG. 3and described above. The flow chart of FIG. 4 is described in terms of3GPP terminology where a DCH is a dedicated channel and a DSCH is adownlink shared channel.

After start, each timeslot is taken (steps 410 and 450) in turn from theDCA1 list and tests (1) to (3)—steps 420 to 440—(described below) areapplied to the timeslots until a timeslot is found for which all testsare passed. If all timeslots fail a new timeslot is provisionallyacquired for DL DCH if the maximum number of DL DCH slots (n_(DL) _(—)_(DCH) _(—) _(MAX)) has not been reached (step 460). In an aspect of thepreferred embodiment of the invention, in such circumstances, the DSCHslot with the smallest timeslot number is sacrificed (provisionally) forDCH (step 470). This policy, when applied across the one or many RNCs,aims to place the DCH slots before the DSCH slots in all cells as far aspossible. This aims to align DCH usage between cells for the reasonsdiscussed above for uplink CAC (FIG. 3). Tests (2) and (3) (steps 480and 490) are then performed with this newly released slot (test (1) isnot required since there is no DCH resource in the new slot). If eithertest fails the CAC is deemed to have failed and the provisionallyacquired timeslot is returned to DSCH usage.

FIG. 5 illustrates slot allocation to DCH and DSCH in accordance withthis feature of the described embodiment of the present invention, anddemonstrates how the DCH slots are held to the lower slot numbers. Ascan be seen:

-   -   initially, at stage 510, all timeslots (1 to 6) are allocated        for DSCH    -   next, at stage 520, DCH users are admitted in timeslot 1    -   next, at stage 530, more DCH users are admitted, requiring        exploitation of timeslots 2 and 3    -   next, at stage 540, all DCH users in timeslot 2 end their calls,        returning this timeslot to DSCH next, at stage 550, more DCH        users are admitted; if they will not fit into timeslot 1 and/or        timeslot 3, timeslot 2 is reclaimed for DCH    -   finally, at stage 560, when all users have ended their calls,        timeslots 1 to 3 are returned to DSCH; all timeslots 1 to 6 are        then, as at stage 510, allocated to for DSCH

The tests in the flow chart of FIG. 4 are described below in terms of3GPP TDD, though these tests are generally applicable to other TDDsystems. Note, these tests are not novel but are included forcompleteness.

Test (1) Availability of Code Division Multiple Access code: Checkdownlink code resource in the timeslot (the RNC must ensure that thereis a spare CDMA code(s) for use by the UE in the downlink). Typically upto 100% of the code space can be used, for example, 16 codes at SF16,but this ceiling may be reduced by the OAM.

Test (2) Availability of base station transmit power: Check that theDPCH transmit power does not exceed the maximum value set. Calculate theexpected transmit power to the UE i from cell j in the timeslot inaccordance with the following formula:

$P_{ij} = \frac{{SIR}_{{tgt},i}{ISCP}_{{i,t}\;}}{{RSCP}_{ij}/P_{{pccpch},j}}$where

-   -   SIR_(tgt,i) is the SIR target for the service of UE i,    -   ISCP_(i,t) is the ISCP measured by the UE i in timeslot t,    -   RSCP_(ij) is the RSCP of the P-CCPCH measured by the UE i to        cell j,    -   P_(pccpch) is the P-CCPCH transmit power of the cell j.

It will be understood by those skilled in the art that the RSCP of theP-CCPCH is a measure of the received power of the broadcast beaconchannel (P-CCPCH) and that this is reported by the UE to the RNC as ameasurement. Thus the term in the denominator of the above equationrelates to the path gain to UE i.

Test (3) Availability of base station transmit power: Check that theNode B can accommodate the additional transmit power in the timeslot:P _(carrier) +P _(ij) <P _(max)where P_(max) is set by the operator in the OAM function and P_(carrier)is determined by a common measurement report passed from the Node B tothe RNC.

It will be understood that the present invention is also applicable tohigh speed DSCH, or HS-DSCH, introduced in Release 5 of 3GPP as a newform of shared channel on the downlink. In principal, the downlink slotsmay accommodate DCH, DSCH and HS-DSCH channels together. The only impacton the DCA is that the maximum number of DL DCH slots (n_(DL) _(—)_(DCH) _(—) _(MAX)) must accommodate the needs of HS-DSCHs carryingconversational or streaming traffic (in the same way as discussed abovefor conversational or streaming traffic on DSCH).

It will be appreciated that the method described above for dynamicchannel assignment for TDD radio communication networks with coexistingdedicated and shared channels may be carried out in software running onprocessors (not shown) in the RNC(s) and/or the UE(s), and that thesoftware may be provided as a computer program element carried on anysuitable data carrier (also not shown) such as a magnetic or opticalcomputer disc.

It will be also be appreciated that the method described above fordynamic channel assignment for TDD radio communication networks withcoexisting dedicated and shared channels may alternatively be carriedout in hardware, for example in the form of an integrated circuit (notshown) such as an FPGA (Field Programmable Gate Array) or ASIC(Application Specific Integrated Circuit).

It will be understood that the scheme for dynamic channel assignment forTDD radio communication networks with coexisting dedicated and sharedchannels described above tends to provide one or more of the followingadvantages:

-   -   DCA1 and CAC uplink algorithm metrics account for intercell        interference, the most significant interference source in TDD        mode systems. This accuracy in the algorithm ultimately leads to        greater capacity.    -   Midcall reallocation according to DCA2 allows coverage and        quality of service to a user to be maintained when a user moves        from the centre of the cell to the cell edge (e.g., a single        timeslot SF8 allocation going to 2 allocated timeslots each with        SF16).    -   Dynamic split between dedicated channel timeslots and shared        channel timeslots allows the network to optimise radio resources        according to traffic type. This will lead to an overall higher        capacity when the network supports both dedicated channels and        shared channels.    -   Alignment of the DCH slots across many cells improves the        usefulness of measurements for DCA/CAC.

It will be appreciated that the above description for clarity hasdescribed embodiments of the invention with reference to differentfunctional units and processors. However, it will be apparent that anysuitable distribution of functionality between different functionalunits or processors may be used without detracting from the invention.For example, functionality illustrated to be performed by separateprocessors or controllers may be performed by the same processor orcontrollers. Hence, references to specific functional units are only tobe seen as references to suitable means for providing the describedfunctionality rather than indicative of a strict logical or physicalstructure or organization.

The invention can be implemented in any suitable form includinghardware, software, firmware or any combination of these. The inventionmay optionally be implemented at least partly as computer softwarerunning on one or more data processors and/or digital signal processors.The elements and components of an embodiment of the invention may bephysically, functionally and logically implemented in any suitable way.Indeed the functionality may be implemented in a single unit, in aplurality of units or as part of other functional units. As such, theinvention may be implemented in a single unit or may be physically andfunctionally distributed between different units and processors.

Although the present invention has been described in connection withsome embodiments, it is not intended to be limited to the specific formset forth herein. Rather, the scope of the present invention is limitedonly by the accompanying claims. Additionally, although a feature mayappear to be described in connection with particular embodiments, oneskilled in the art would recognize that various features of thedescribed embodiments may be combined in accordance with the invention.In the claims, the term comprising does not exclude the presence ofother elements or steps.

Furthermore, although individually listed, a plurality of means,elements or method steps may be implemented by e.g. a single unit orprocessor. Additionally, although individual features may be included indifferent claims, these may possibly be advantageously combined, and theinclusion in different claims does not imply that a combination offeatures is not feasible and/or advantageous. Also the inclusion of afeature in one category of claims does not imply a limitation to thiscategory but rather indicates that the feature is equally applicable toother claim categories as appropriate. Furthermore, the order offeatures in the claims do not imply any specific order in which thefeatures must be worked and in particular the order of individual stepsin a method claim does not imply that the steps must be performed inthis order. Rather, the steps may be performed in any suitable order. Inaddition, singular references do not exclude a plurality. Thusreferences to “a”, “an”, “first”, “second” etc do not preclude aplurality.

The invention claimed is:
 1. A method performed by a wireless network,the method comprising: dynamically allocating, by the wireless networkto a user equipment (UE) in a cell, a timeslot to a downlink dedicatedchannel for a call, wherein the timeslot has a lowest available timeslotnumber in a frame; monitoring, by the wireless network, the call andreallocating the call to a different timeslot substantially midcall,wherein the different timeslot has a highest quality rank in the cell;allocating, subsequently by the wireless network, another timeslot for adownlink shared channel in the cell, wherein the another timeslot has ahighest available timeslot number; and wherein allocation of timeslotsto the downlink dedicated channel are prioritized over allocation oftimeslots to the downlink shared channel.
 2. The method of claim 1,wherein the timeslot or the different timeslot have a dynamicallyassigned maximum number.
 3. The method of claim 1 further comprising:allocating, by the wireless network, a predetermined number of timeslotsfor the downlink dedicated channel.
 4. The method of claim 1, whereinthe timeslot or the different timeslot is used by another dedicateddownlink channel by another UE.
 5. The method of claim 1, wherein thereallocation is performed based on a location of the UE in the cell. 6.The method of claim 1, wherein the timeslot or the different timeslot isallocated based on intercell interference signals.
 7. The method ofclaim 1, wherein the timeslot or the different timeslot is allocatedbased on interference signal code power or signal to interference ratioassociated with the timeslot or the different timeslot.
 8. The method ofclaim 1, wherein the different timeslot is added, substantially midcall,to the timeslot for the call while a power level for the call is heldsubstantially constant.
 9. The method of claim 1, wherein the wirelessnetwork is configured to provide time division duplex (TDD)communication.
 10. A wireless network characterized in that: thewireless network is configured to allocate, dynamically to a userequipment (UE) in a cell, a timeslot to a downlink dedicated channel fora call, wherein the timeslot has a lowest available timeslot number in aframe; the wireless network is configured to monitor the call andconfigured to reallocate the call to a different timeslot substantiallymidcall, wherein the different timeslot has a highest quality rank inthe cell; the wireless network is further configured to allocate,subsequently, another timeslot for a downlink shared channel in thecell, wherein the another timeslot has a highest available timeslotnumber; and wherein allocation of timeslots to the downlink dedicatedchannel are prioritized over allocation of timeslots to the downlinkshared channel.
 11. The wireless network of claim 10, wherein thetimeslot or the different timeslot have a dynamically assigned maximumnumber.
 12. The wireless network of claim 10 further characterized inthat: the wireless network is configured to allocate a predeterminednumber of timeslots for the downlink dedicated channel.
 13. The wirelessnetwork of claim 10, wherein the timeslot or the different timeslot isused by another dedicated downlink channel by another UE.
 14. Thewireless network of claim 10, wherein the reallocation is performedbased on a location of the UE in the cell.
 15. The wireless network ofclaim 10, wherein the timeslot or the different timeslot is allocatedbased on intercell interference signals.
 16. The wireless network ofclaim 10, wherein the timeslot or the different timeslot is allocatedbased on interference signal code power or signal to interference ratioassociated with the timeslot or the different timeslot.
 17. The wirelessnetwork of claim 10, wherein the different timeslot is added,substantially midcall, to the timeslot for the call while a power levelfor the call is held substantially constant.
 18. The wireless network ofclaim 10, wherein the wireless network is configured to provide timedivision duplex (TDD) communication.